The goal of this research proposal is to test the hypothesis that human fetal oxygenation is a function of the placental surface area available for diffisional exchange, that maternal ventilation and erythropoiesis are functions of the metabolism of the fetal-placental unit; and that during constant adequate maternal nutrition, placental growth is function of maternal oxygenation. The testing of these 3 hypotheses will improve our understanding if two clinical entities - idiopathic intrauterine growth retardation and pregnancy induced hypertension. Both these clinical problems appear to be associated with decreased functional placental tissue resulting in inadequate fetal growth and failure of the maternal organism to make the compensatory increase in red cell mass, resulting in an inability to adequately increase cardiac output and therefore an inability to adequately perfuse the uteroplacental bed.